The progress of mobile station techniques have brought and will bring to the marketplace new and versatile models, in which new requirements are placed on the antennas: for instance, the antenna must operate on two frequency ranges, such as the 900 MHz and 1.8 GHz ranges; the bandwidth or bandwidths must be relatively wide; the radiation and reception characteristics must be rather good when the device and the antenna are in different positions and in different locations regarding external objects; and yet the antenna must be relatively small and compact.
There are previously known antenna structures suitable for mobile stations which have a wide bandwidth or which operate on two frequency ranges.
Antennas based on a helix:
Within a helix element there is placed a rod element resonating at a different frequency, whereby the rod element is fed separately or in common with the helix element, or it could be a parasitic rod. Disadvantages of such structures are the relatively high manufacturing costs and clearly deteriorated characteristics, when the antenna is located or turned close to the frame of the device.
Microstrip structures:
On the surfaces of and possibly within a dielectric plate there are radiating conductor areas, of which one or more can be a feed area, and of which one or more can be parasitic areas. The conductor areas can also be designed so that they contain one or more gaps acting as radiators. A disadvantage of most microstrip structures are their relatively narrow bandwidths. This disadvantage is less pronounced in structures containing parasitic elements, but then a disadvantage will be the relatively large size of the structure. The characteristics of microstrip antennas are also subject to drift, and the costs of structures fulfilling said requirements are rather high.
Chip structures:
Within a dielectric monolithic body there are one or more conductors, for instance with a meander form, which radiate at different frequencies. A disadvantage of these structures are the relatively narrow bandwidths, if the bands are separate.